Method overflow

include/asio/basic_socket_streambuf.hpp:468–540

  }

  int_type overflow(int_type c)
  {
#if defined(ASIO_WINDOWS_RUNTIME)
    ec_ = asio::error::operation_not_supported;
    return traits_type::eof();
#else // defined(ASIO_WINDOWS_RUNTIME)
    char_type ch = traits_type::to_char_type(c);

    // Determine what needs to be sent.
    const_buffer output_buffer;
    if (put_buffer_.empty())
    {
      if (traits_type::eq_int_type(c, traits_type::eof()))
        return traits_type::not_eof(c); // Nothing to do.
      output_buffer = asio::buffer(&ch, sizeof(char_type));
    }
    else
    {
      output_buffer = asio::buffer(pbase(),
          (pptr() - pbase()) * sizeof(char_type));
    }

    while (output_buffer.size() > 0)
    {
      // Check if we are past the expiry time.
      if (traits_helper::less_than(expiry_time_, traits_helper::now()))
      {
        ec_ = asio::error::timed_out;
        return traits_type::eof();
      }

      // Try to complete the operation without blocking.
      if (!socket().native_non_blocking())
        socket().native_non_blocking(true, ec_);
      detail::buffer_sequence_adapter<
        const_buffer, const_buffer> bufs(output_buffer);
      detail::signed_size_type bytes = detail::socket_ops::send(
          socket().native_handle(), bufs.buffers(), bufs.count(), 0, ec_);

      // Check if operation succeeded.
      if (bytes > 0)
      {
        output_buffer += static_cast<std::size_t>(bytes);
        continue;
      }

      // Operation failed.
      if (ec_ != asio::error::would_block
          && ec_ != asio::error::try_again)
        return traits_type::eof();

      // Wait for socket to become ready.
      if (detail::socket_ops::poll_write(
            socket().native_handle(), 0, timeout(), ec_) < 0)
        return traits_type::eof();
    }

    if (!put_buffer_.empty())